Aluminum's not supposed to react like this.

[blackcote]

We got some cast gun pieces to anodize this past weekend. We've had some success with cast in the past, but this was a total disaster this time as we didn't even get to try to anodize. We put them in cleaner and they got smutty as expected, then to the deox and it wouldn't toucht the smut.... but it could be wiped off. So we wiped them down and we put them in stripper for a few minutes as they were bead blasted and that seems to help in most cases. But when doing so... the parts reacted severely to the stripper solution. We thought it was a bit odd, but carried on. Back to the deox to remove smut and nothing. Didn't even touch it. One piece in particular started flakng stuff off in the deox... that was really odd. took that one out quite quickly and noticed that sploches of areas had smut and other didn't... hence the flakes. Ok apparently something was on the out side (almost like a plating). Back to the bead blaster to remove the remaining covering. then tried stripping and the reaction was much more normal. So we eventually try to stick this piece in the anodize solution and there is a violent reaction almost like sticking aluminum in a hot black oxide tank. So we're scratching the attempt at anodizing these pieces. It's really disappointing as we have a .22 short barrel that would have looked real nice in anodize. Now we have to resort to painting.

So anyway my question if anyone has any idea is what is in this alloy that reacts to a sulfuric acid solution this way? When I feel the weight of the piece in my hand it seems heavier than aluminum so I did some rough weight calculations with water displacement to try to make sure that it wasn't steel and if I did them right... it confirmed that it was not steel alloy but it feels like there is something more dense than aluminum in it as it feels heavier than I think it should. Not very scientific, but it's all I got.

[rclint]

Re: Aluminum's not supposed to react like this.

What gun was it from ?

I think you have something other than aluminum, a lot of 22 rifles (cheaper ones) are made from no telling what

they grey smut that the desmut wouldn't touch is prob silicon

Clint

[RedRiver]

Re: Aluminum's not supposed to react like this.

Is it cast aluminum from over seas? The quality of the cast might be the problem. Poor quality control and a much higher silicone content than expected could certainly be the culpret in this case.

Just my $0.02

Cheers!
- Dan

[mcaswell]

Re: Aluminum's not supposed to react like this.

Sounds like a type of pot metal you have there. No way that is going to anodize.

Try dropping a little acid on the part. If it fizzes violently, it's pot metal. Only thing you can do is plate it with Flash Copper.

[blackcote]

Re: Aluminum's not supposed to react like this.

What is the density of pot metal? Would it be no heavier than aluminum and does it not have magnetic properties?

The origin is unknown as th gun was already tore down when we got the parts. Any way to test for material of these parts other than contaminating our anodizing tanks?

[rclint]

Re: Aluminum's not supposed to react like this.

Sounds like a type of pot metal you have there. No way that is going to anodize.

Try dropping a little acid on the part. If it fizzes violently, it's pot metal. Only thing you can do is plate it with Flash Copper.

test by above, I don't think you are dealing with aluminum, I have anodized a lot of cast aluminum and never seen a reaction like you are talking about, the main problem with cast aluminum is a dark smut that will not tkey dye, or I should say show dye very well if any at all.

I have been working with cast a good bit, here is a part that i recently done, the trigger group, receiver are cast andozed and dyed black, the time on anodizing these parts is about 1/3 of the time calculated using the LCD method, I calculate eveyrthing out using the LCD method, but use par for the actual anodizing time and have no idea how thick of coatings I'm getting.

The trigger is good aluminum, 6xxx series I think, and takes dye like a hoover heha

Picture didn't upload here is a link
http://img.photobucket.com/albums/v4...eceiver004.jpg

Clint

[adavislock]

Re: Aluminum's not supposed to react like this.

Justin,
I, too have had problems as you described. As a gun refinisher I feel your pain. We had a Winchester .22 reciever that acted in a similar manner, our solution was to powder coat the darn thing. On another gun, a revolver we thought was aluminum, no dice. This was some exotic metal ( probably with some magnesium ) that actually took a cold blue however we were afraid to run it through the hot tanks so we wound up powder coating it also. Evidently with firearms there are many variables to keep us on our toes. I do have a question for you. Are you able to obtain a gloss finish on anodized pieces? The parts we have tried lose their gloss in the anodizing process (probably from the acid-at least thats the case when we acid dip some parts before hot bluing). Any thoughts?

[blackcote]

Re: Aluminum's not supposed to react like this.

I know what you mean about many varied materials in fire arms. Winchester recievers seem to give a fair amout of trouble coming out with a redish tint or an uneven finish... sort of spotty looking. Anyway No gloss finishing it's sort of matte finish that looks dark grey. a post treatment of oil really seams to bring out the black. and give it a nice sheen but certainly not glossy to match the buffed barrels. The problem is two fold I think. It's the anodize process that takes away from the gloss as your building a bunch of tiny holes on the part for dye absorbtion and protection. Then on top of that your trying to do it on cast which is notoriously prone to dye problems. If we had a way to measure pore size we could adjust parameters to the process to get results like we do from good aluminum. But I suspect it would still be somewhat limited to the material properties of the cast.

[rclint]

Re: Aluminum's not supposed to react like this.

When the aluminum in cast is converted over to aluminum oxide and the silicon, copper, etc etc left behind the aluminum is converted is where the grey smut comes from, you can adjust the times anodizing and overcome part of this but so far I have not ben able to get a perfect finish other than black

Clint